Constant voltage rectifier circuit



y 1940- Q A. CHRISTIE 2,201,979

CONSTANT VOLTAGE RECTIFIER CIRCUIT Filed May 2, 1938 Fig.2 Fly6 3W1.

Fig. 3 Fig.4 F g AL/ RED CHE/5775 CZ-gk-W Patented May 28, 1940 UNITEDSTATES PATENT OFFICE CONSTANT VOLTAGE RECTIFIER CIRCUIT cessors inoffice Application May 2, 1938, Serial No. 205.517

1 Claim.

(Granted under the act of March 3, 1883, as amended April 30, 1928; 370O. G. 757) This application is made under the act of March 3, 1883, asamended by the act of April 30, 1928, and the invention hereindescribed, if patented, may be manufactured and used by or for theGovernment of the United States of America for governmental purposeswithout the payment to me of any royalty thereon.

This invention relates to electrical rectifiers and is more particularlyconcerned with such rectifiers which employ a thermionic valve.

One of the objects of this invention is the provision of such arectifier for use with instruments which require a constant voltagepotential output under varying conditions of input current such as isrequired by the Tag-Heppenstall moisture meter. See U. S. Patent No.1,826,247.

One of the advantages of this invention over other types of rectifiersis that it does not require for its successful operation anytransformers, auxiliary batteries, or other parts heretofore essential.

The following description considered together with the accompanyingdrawing will fully disclose this invention, its construction andoperation of parts and further objects and advantages thereof will beapparent.

In the drawing:

Figure l is a diagram of the circuit employed in this invention in itssimplest form.

Figure 2 is a diagram of a modification of the circuit shown in Figure1.

Figures 3, 4, 5 and 6 are facsimile reproductions of oscillograph curveshereinafter fully explained.

Referring with more particularity to Figure 1, an ordinary rectifiertube 3 having the usual heater filament 4, cathode 5, and plate or diode6, is of the half-wave type. The filament 4 is energized by the inputalternating current through a line-cord resistor l and is controlled bythe toggle switch 8. The diode 6 of the rec tifier tube 3 is connectedwith the lead of the input between the line resistor and the inputsource 9. The cathode 5 is connected to the positive of the output leadthrough a choke coil I l. The negative lead of the output is connectedto the filament circuit of the rectifier tube. The capacitance or filtercondenser Ill is connected across the output of the rectifier tube andan electronic voltage regulator l2 having a cathode l2 A and an anode 12B is shunted across the output of the filter system, which systemcomprises the capacitance l0 and choke l I. It is to be understood,however, that additional filter sys" tems may be employed to reduceripple characteristics. The electronic voltage regulator !2 may be ofany of the types in common use, preferably the voltage regulator tubedescribed in U. S. Patent No. 1,760,524.

For a constant 90 volt potential, such as is required by theabove-mentioned Tag-Heppenstall moisture meter, the voltage regulatortube commercially designated as the 874 is found to be satisfactory.Also, better and more economical results are obtained by using a voltagedoubler rectifier tube, instead of an ordinary rectifier tube, andmutually connecting the two diodes and the two cathodes, respectively.These connections are accomplished outside of the tube. With thesemodifications the circuit is substantially as shown in Figure 2. In thisfigure the cathodes l3, l3 of the voltage doubler rectifier tube M, aremutually connected by means of the wire [5, and the two diodes l6, iiiare mutually connected by means of the wire IT. The electronic voltageregulator tube i8 is shunted across the output with the electrodes 19and 20, said electrodes being the anode and cathode, respectively, ofsaid regulator tube. It is preferable, however, to utilize twoadditional terminals 2|, 22, on said voltage regulator tube l3, as aswitch. These terminals are mutually connected internally by means of awire 23 so that by placing these terminals in series with the filamentcircuit of the rectifier tube the system will not work unless thevoltage regulator tube is present in the circuit. This prevents anydamage to the system which may result from the absence of the tube.

Where it is desired to maintain a voltage of 90 volts from analternating potential of substantially 90 to- 120 volts, theabove-mentioned specified tubes are preferred and in addition theretothe capacitance or filter condenser i0 should have a working voltage of250 volts. The line-cord resistor should be of sufiicient value toreduce the current for the filament of the rectifier tube to asatisfactory limit.

If desired the capacitance H3 may be used on the choke output instead ofthe choke input. Also, it may be found advantageous in some cases toemploy two capacitances, one on the input and the other on the output ofsaid choke. It is to be understood that such modifications are withinthe scope of this invention.

As it is above stated, one of the advantages of this invention is thatit does not require any transformers, auxiliary batteries or other partsheretofore considered necessary in other types of rectifiers. This isthe essence of the invention. ing circuits employ electronic voltageregulator tubes or, as they are commonly termed, glow For example, whileother types of rectifydischarge tubes, they do not employ a choke inseries with the tube. This choke serves to insure and maintain the glowtube with a safe operating current above its extinction potential and italso reduces output ripple characteristics. Ihis is very essentialespecially in half-wave rectification because an oif-phase-in-phasecycle is delivered by the output of the rectifier tube and unless someprovision is made the glow tube will become damaged. While a pureresistance might be used to protect the tube from damage, it will notmaintain the required voltage for continuous operation of the glow tube.

To more clearly illustrate the distinguishing characteristics of thisinvention over other ha1iwave rectification circuits, experiments havebeen conducted using an oscillograph to show the alternating currentcomponent of the output of various rectification circuits in contrast tothe circuit of the present invention. Figure 3 shows the characteristiccurve obtained using an equivalent pure resistance instead of the chokeand an equivalent bleeder resistance instead of the glow tube in thecircuit illustrated in Figure 2. Figure 4 is the result of the samecircuit with the bleeder resistance replaced by a glow tube. Figure 5 isthe result of using a choke in combination with the bleeder resistanceand Figure 6 is the characteristic curve of the present invention wherethe choke in combination with a glow tube demonstrates substantially adirect current characteristic approaching very closely the kind of acurrent norm-ally drawn from batteries. All of the above results wereobtained under identical conditions of input and output and underexactly the same scale ratios of the oscillograph. In all of these fourfigures the vertical displacement represents the voltage of thealternating current component of the output and the horizontaldisplacement is a function of time. Accordingly, each figure representsa complete wave cycle. From these facsimiles it may be seen that thevoltage of the alternating current component of the output in Figure 6is practically negligible in comparison to those of Figures 3, 4 and 5.

It is to be understood that while the above in vention has beendescribed as being applicable to an alternating current input it mayalso be employed with direct current inputv Having thus described myinvention, I claim:

A constant voltage rectifier consisting of an output circuit and aninput circuit in combination with a thermionic valve tube, said tubehaving twin cathodes mutually connected exterior to said tube, twindiodes mutually connected exterior to said tube, and a filament circuitenergizable by said input circuit through a line cord 'esistor; a glowdischarge tube and a condenser in parallel with said output circuit anda choke coil in series with said output circuit between said condenserand said glow discharge tube, whereby said glow discharge tube ismaintained and insured with a safe operating current above itsextinction potential, that part of the circuit between the glowdischarge tube and the load of the circuit being shuntlcss andnon-inductive.

ALFRED CHRISTIE.

